This invention relates to an automatic lighting circuit control device responsive to the presence of a person within the space to be lighted.
A fundamental approach to presence or motion detection is commonly known as a "Doppler Shift" detector. Systems of this type radiate electromagnetic energy of a predetermined frequency, typically ultrasonic, into the area to be protected and the reflected energy is detected by a suitable conventional receiver. Any movement of an object within the protected area results in a shift between the frequency of the transmitted and detected energy known as the "Doppler Shift". Detection of a Doppler Shift may be utilized to enable an alarm to indicate the presence of an object in motion within the protected space.
Doppler Shift principles have been applied to the control of lighting circuits through the use of a time delay system. See, e.g. U.S. Pat. No. 2,393,014 to Bartholy and U.S. Pat. No. 3,459,961 to Ravas. These and similar patents relating to lighting circuit control devices generally do not distinguish between the requirements of a light control system and an alarm control system. While there is a certain similarity between the requirements for the intrusion detection and lighting control, the requirements of the two systems are not totally compatible in commercial applications, and difficulties have been encountered in the actual use of such systems.
For example, it has been found that triggering of the alarm at a first possible indication of motion is generally intolerable in an intrusion alarm device, in that each false alarm requires inquiry to determine if, in fact, the premises have invaded by an intruder. Further, alarm devices do not require repeated triggering. As a result, alarm devices typically rely on long time integration of the received signals, careful amplitude thresholding, and careful selection of one or more frequencies for detection. Other systems delay an alarm sufficiently to compare the negative Doppler Shift with the positive Doppler Shift to determine whether a symmetrical pattern noncharacteristic of human motion is present.
In certain applications in lighting control systems, it is not generally necessary for the lights to respond instantaneously upon the entrance of a person into the room, but a response is necessary within a short time period thereafter. Further, it is critical in lighting systems that lighting be maintained for only so long as the space is occupied. Thus, the presence of motion must continue to be detected. Also the presence of motion has to be recognized and detected at any spot within the entire monitored space, as contracted with certain critical entry areas.
In dealing with these fundemental differences between alarm and lighting control system, it has been proposed to use a filtering, sensitivity adjusting, amplifying control which automatically adjusts to the amplitude and excursion characteristics of the reflected energy. For example, U.S. Pat. No. 4,193,055 to C. Barnum relies on the fact that human motion typically produces erratic Doppler signals whereas noise typical of air conditioners and the like typically produces a fairly consistent Doppler for an extended period of time. Integration of the signals as typically used in intrusion alarm systems is eliminated to avoid masking a human motion signal, particularly when the motion detected overlaps with a high noise level signal. Such devices automatically adjust the sensitivity level of the system inversely with the amplitude after a predetermined time delay. The time delay permits short term amplitude gain, but suppresses the gain of constant amplitude signals to filter out long term constant noise. Thus, the sensitivity of the system in a noisy environment is automatically lowered when ambient noise is at an appreciable level, and increased in a low noise environment.
It is accordingly an object of the present invention to provide a novel lighting control system and method which obviates the problems associated with the prior art systems.
It is also an object of the present invention to provide a novel method and system for controlling the lighting in spaces as a function of the presence of humans therein.
It is another object of the present invention to provide a novel method and system for the selective zoning of lighting control within a space.
It is still another object of the present invention to provide a novel method and system for eliminating the need for mounting transmitters and receiver in pairs in close proximity to each other.
It is a further object of the present invention to provide a novel method and system for ultrasonic sensing of the presence of personnel in a space in which the receiver and transmitter are mounted orthogonally to each other.
It is yet a further object of the present invention to provide a novel system and method in which the vibration upon energization of the transmitter is prevented from affecting the operation of the receiver.
It is yet still a further object of the present invention to provide a novel method and system for ultrasonic detection which detects the amplitude modulation of the ultrasonic energy within a space as contrasted with the Doppler Shift frequency of the reflected energy.
These and other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains and may be more clearly understood from the following detailed description of the preferred embodiment when read in conjunction with the appended drawings.